Wideband directional filter device

ABSTRACT

A wideband directional filter device comprises two ring-shaped travelling wave cavity resonators having different circumferential lengths and arranged in substantially the same plane with E-planes at the mutually facing inner side portions disposed in proximity to each other; a semi-circular waveguide whose flat base has its underside disposed to bridge the mutually facing portions of H-planes on one side of the cavity resonators; two rectangular waveguides located closely below each H-plane on the other side of the cavity resonators; and directional couplers provided at the oppositely facing wall portion between the rectangular waveguides and the cavity resonators as well as at the oppositely facing wall portion between the cavity resonators and the semi-circular waveguide. According to the wideband directional filter so constructed, upon reception individually resonated signal components are separated, by the cavity resonators having different circumferential lengths, from a group of composite wideband signals having different central frequencies higher than the micro-wave band transmitted through the semi-circular waveguide and each derived from the associated one of the two rectangular waveguides. Upon transmission two signal components having different central frequencies higher than the microwave band are composed through a signal path comprised of the two rectangular waveguides, the two cavity resonators and the semi-circular waveguide.

United States Patent 91 Ohi et al.

[ WIDEBAND DIRECTIONAL FILTER DEVICE [75] Inventors: Kunio Ohi, Tokyo; Sadalguni M W Shimada; Isao Ohtomo, both of Yokohama, all of Japan [73] Assignees: Nippon Telegraph and Telephone Public Corporation; Hitachi Electronics Co., Ltd., both of Tokyo, Japan [22] Filed: Dec. 20, 1972 [21] Appl. No.: 317,051

[30] Foreign Application Priority Data Dec. 24, 197] Japan 46-104658 [52] US. Cl. 333/10, 333/73 W [51] Int. Cl. 1101p 5/14, HOlp 1/20 [58] Field of Search 333/10, 73 R, 73 S, 76

[5 6] References Cited UNITED STATES PATENTS 2.854.636 9/1958 Marie 333/l0 3.668,565 6/l972 Tuchen 333/73 W Primary Examiner-Archie R. Borchelt Assistant ExaminerWm. H. Punter Attorney, Agent, or FirmFlynn & Frishauf [451 Apr. 9, i974 5 7] ABSTRACT A wideband directional filter device comprises two ring-shaped travelling wave cavity resonators having different circumferential lengths and arranged in substantially the same plane with E-planes at the mutually facing inner side portions disposed in proximity to each other; a semi-circular waveguide whose flat base has its underside disposed to bridge the mutually facing portions of H-planes on one side of the cavity resonators; two rectangular waveguides located closely below each H-plane on the other side of the cavity resonators; and directional couplers provided at the oppositely facing wall portion between the rectangular waveguides and the cavity resonators as well as at the oppositely facing wall portion between the cavity resonators and the semi-circular waveguide. According to the wideband directional filter so constructed, upon reception individually resonated signal components are separated, by the cavity resonators having different circumferential lengths, from a group of composite wideband signals having different central frequencies higher than the micro-wave band transmitted through the semi-circular waveguide and each derived from the associated one of the two rectangular waveguides. Upon transmission two signal components having different central frequencies higher than the microwave band are composed through a signal path comprised of the two rectangular waveguides, the two cavity resonators and the semi-circular waveguide.

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PATENTEDAPR 9 1914 SHEET 5 OF 5 FIGS WIDEBAND DIRECTIONAL FILTER DEVICE The present invention relates to a wideband directional filter device, and more particularly to a wideband directional filter device suitable as a channel dropping filter in a frequency branching or separation filter system for millimetric wave communication. An arrangement of FIG. 1 is shown as a representative example of such conventional wideband directional filter devices.

On one side of two ring-shaped travelling wave cavity resonators 1 l and 12 superposed on each other a semicircular waveguide 13 is disposed with the underside of its flat base and on the other side of the cavity resonators a rectangular waveguide 14 is disposed. In those mutually facing wall portions of the cavity resonator l l and the semi-circular waveguide 13 which are situated along the axis of the semi-circular waveguide and in the mutually facing Wall portions (not shown) of the cavity resonator I2 and the rectangular waveguide 14, there are respectively provided directional couplers consisting of a plurality of circular holes bored at an interval of about a quarter of its guide wavelength. Likewise, multi-holes 16 are bored in the metal plate sandwiched between the cavity resonators 11 and 12. With the wideband directional filter device so constructed, when composite signals having different central frequenciesfl ,f2,f3 .fn are applied from one port 131 of. the semi-circular waveguide 13 and the circumferences of the cavity resonators 11 and 12-are designed to have a length equal to an integral multiple of the guide wavelength of the central frequency, for example, fl of any of the aforesaid composite signals, then the signal fl after being resonated by the cavity resonators 11 and 12 is drawn out from either, for example 141, of two ports 141 and 142 of the rectangular waveguide 14. The remaining composite signals f2 to fn are travelling through the other port 132 of the semicircular waveguide 13 without any influence from the cavity resonators. Therefore, when a plurality of wideband directional filter devices are connected in a cascade configuration, then each signal component of the aforesaid composite signals fl to fn can individually be filtered out. From this it will be appreciated that if the signal path is reversely traced, then each individual signal component can be transmitted in a composite form.

According to the wideband directional filter device so constructed, in the frequency range higher than a microwave band such as particularly a millimetric or semi-millimetric wave band, the semi-circular waveguide generally has a wideband characteristic at a lower loss than that of a rectangular waveguide. Accordingly, the semi-circular waveguide is suitable to separate or compose a wideband signal consisting of a group of signals having different central frequencies. In addition, the wideband directional filter device of FIG. 1 also has a function of converting transmitted signal modes, namely, converting the dominant mode TE of the semi-circular waveguide to the dominant mode TE of the rectangular waveguide or vice versa.

With the wideband directional filter device having such construction, multi-holes are used as directional couplers between the semi-circular waveguide and the cavity resonators as well as between the rectangular waveguide and the cavity resonators. Therefore, it is only possible, as is well known to those skilled in the art, to attain a 3dB bandwidth which bears the ratio of less than 1 percent to a centralfrequency, thus presenting difficulties in applications which demand a higher ratio. The reason is that the size and number of the coupling holes are restricted. Since it is necessary to transmit an electromagnetic wave only in one direction, each coupling hole is required to be arranged to have an interval equal to substantially a quarter of its guide wavelength as mentioned above. Therefore, when a standard-dimensioned semi-circular and rectangular waveguides for transmitting a signal of, for example, SOGHZ are considered, then a center-to-center spacing of each coupling hole will be about 2mm. In order to prevent an overlap of each coupling hole and keep a mechanical strength, the inner diameter of each coupling hole must be less than 2mm. Since the length of the circumference of the cavity resonator cannot be unlimitedly increased to avoid an undesired resonance, the number of the coupling holes is restricted in this respect.

The semi-circular waveguide generates a plurality of spurious modes in addition to an inherent dominant mode of TE If, therefore, the semi-circular waveguide has a poor impedance matching with the coupling surface (E-plane) of the cavity resonator, then there will result the drawback of generating various spurious modes.

Accordingly, the object of the present invention is to provide a wideband directional filter device suitable as, for example, a channel dropping filter in a frequency branching filter device particularly for millimetric and- /or semi-millimetric wave band communication.

SUMMARY OF THE INVENTION According to the present invention, there is provided a wideband directional filter device design to separate in reception any desired signal component from a group of composite wideband signals having different central frequencies which are higher than that of the microwave region and conversely in transmission to compose individual signal components to transmit the composed wideband signals, the improvement being that said wideband directional filter device comprises a semi-circular waveguide connected to a transmission line for transmittingsaid group of composite wideband signals; two ring-shaped travelling wave cavity resonators disposed in substantially the same plane to have the mutually facing inner side walls near the two portions on the flat wall of said semi-circular waveguide positioned substantially symmetrical with respect to the axis thereof and each having a circumferential length equal to an integral multiple of the guide wavelength of each central frequency of any two different signal components included in said group of composite wideband signals; two rectangular waveguides each having its wall portion disposed in proximity to the associated one of said two cavity resonators; and directional couplers disposed in at least the mutually facing wall portions between said two rectangular waveguides and said two cavity resonators as well as between said two cavity resonators and said semi-circular waveguide.

The present invention can be more fully understood from the following detailed description when taken in connection with the accompanying drawings, in which:

FIG. 1 is a perspective view, partly broken away, showing a conventional wideband directional filter device;

FIG. 2 is a schematic block diagram of a millimetric or semi-millimetric wave communication system to which a wideband directional filter device according to the present invention is applicable;

FIG. 3 is an exploded, perspective view, partly broken away, showing one embodiment of a wideband directional filter device according to the present invention;

FIG. 4 shows the state in which there are cascade connected a plurality of wideband directional filter devices shown only one in FIG. 3;

FIG. 5 is a characteristic curve representation showing the results of experiments conducted in a manner that a semi-circular waveguide and both rectangular waveguides are superposed, as shown in FIG. 6, to the exclusion of ring-shaped cavity resonators from the wideband direction filter of FIG. 3;

FIG. 7 is a perspective view, partly broken away, showing the essential part of a modification of a wideband directional filter according to the present invention; and

FIG. 8 is an exploded, perspective view, partly broken away, showing another embodiment according to the present invention.

In order to futher facilitate an understanding of the scope of the present invention, let us explain a schematic construction of a 40-80Gl-Iz millimetric wave band (or semimillimetric wave band) communication system as shown in FIG. 2 which is intended for using as a channel dropping filter a wideband directional filter device according to the present invention. A group of composite signals having different central frequencies falling within 40-80HGZ are supplied, for example, through a transmission line 21 using a circular waveguide of about 5lmm in diameter to a bandsplitting fil' ter 22 having a central frequency substantially at the middle i.e. 6OGHz, of the whole frequency band width of 40-8OGHz and adapted to be splitted into a low band side signal component of 40-6OGHZ and a high band side signal component of 60-80GHZ. The low band side signal component of 40-6OGHZ so filtered is then supplied to a transmission/reception filter 23 having a central frequency substantially at the middle, i.e., SOGHz, of the frequency band width of 40-6OGl-Iz and adapted to be filtered into a signal component of 40-50Gl'lz (for reception) and a signal component of 50-60GHz (for transmission). Likewise, the high band side signal component of 608OGHz so filtered by the band-splitting filter 22 is supplied to a transmission/- reception filter 24 having a central frequency substantially at the middle, i.e., 70GI-Iz', of the frequency band width of 60-80GHz and adapted to be filtered into a signal component of 60-7OGHz (for reception) and a signal component of 70-80GH2 (for transmission). In two transmission paths 25 and two reception paths 26 branched by the respective two transmission/reception filters 23 and 24, repeaters for 12 channels (thus 24 channels for reception and 24 channels for transmission) at a frequency interval of 0.8GHz as shown in FIG. 2 are sequentially connected in a cascade configuration, each having a channel dropping filter, to be later described. At the other end of the four repeater sections there are disposed transmission/reception filters 23 and 24, a band-splitting filter 22 and a circular waveguide path 21 having the same arrangement as mentioned above.

A wideband directional filter device according to the present invention is designed to be suited as a channel dropping filter included in a frequency separation filter system comprising said channel dropping filter, transmission/reception filter and band-splitting filter for the millimetric or semi-millimetric wave band communication system. In a communication system as shown in FIG. 2, use is made of, for example, a PCM-4-phase PSK modulation system and it is desirable to use about 400MB as a pulse repetition rate fr. In order to attain such a high speed information transmission, a frequency interval Bs of about 800MHz (Bs/fr=2) as above described will be required between the adjacent repeater channels. In a repeater channel having a central frequency of SOGHZ, a 3dB band width relative to the central frequency will be 8OOMl-Iz/5OGI-Iz=l .6 percent. Accordingly, it is difficult to obtain a3dB bandwidth which bears such a ratio to the central frequency using a conventional wideband directional filter device as shown in FIG. 1.

FIG. 3 is an exploded view, partly broken away, showing a wideband directional filterdevice according to the present invention suitably manufactured as a channel dropping filter to be installed in each repeater for a millimetric or semi-millimetric wave band communication system as shown, for example, in FIG. 2.

The wideband directional filter device according to the present invention comprises, as shown in FIG. 3, three substantially equally-dimensional, square-shaped metal blocks manufactured in a manner to be later described, the upper and lower metal blocks 31 and 32 being relatively thick and the intermediate metal block 33 disposed between the metal blocks 31 and 32 relatively thin. In the central portion of the bottom of the upper metal block a semi-circular waveguide 34 extending from one end to the opposite end of the upper metal block 31 is bored. In those top and bottom portions of the intermediate metal block 33 which are situated at both the sides of the axis of the semicircular waveguide 34 of the upper metal block there are provided two ring-shaped travelling wave cavity resonators 35 and 36 which are adjacent to each other and have different circumferential lengths.

In each partition wall of the two layered cavity resonators are provided multi-holed directional couplers 37 and 38 which are formed in a manner to be later described. In the upper wall of the lower metal block 32 two adjacent substantially U-shaped grooves adjacent are provided in substantially a mirror imaged relation with respect to the axis of the semi-circular waveguide 34. On the upper wall of the lower metal block 32 an electrically conductive metal plate 39 forming a top wall of the two U-shaped grooves and having a thickness of about 0.1mm is disposed to form two substantially U-shaped rectangular waveguides 40 and 41.

In those portions of the metal plate 39 corresponding to the mutually faced adjacent portions of the two rectangular waveguides, transverse multi-slitted directional couplers 42 and 43 are formed in a manner to be later described. Likewise, a metal plate 44 of the same material and dimension as the metal plate 39 forming a bottom wall of the semi-circular waveguide 34 is disposed on the bottom of the upper block 31 to form transverse multi-slitted directional couplers 45 and 46 situated adjacent to each other on both the sides of the axis of the semi-circular waveguide 34.

The wideband directional filter device according to the present invention is formed by superposing three metal blocks 31, 32 and 33 in an unitary fashion, in a manner that each of two directional couplers 45 and 46 consisting of multi-slits provided in the semi-circular waveguide 34 is aligned, through the mutually facing inner wall portions of the directional couplers 37 and 38 of the ring-shaped cacity resonators 35 and 36, with the directional couplers 42 and 43 consisting of multislits provided in the respective rectangular waveguides and 41.

According to the wideband direction filter device 30 so constructed, the ring-shaped cavity resonators 35 and 36 and the rectangular waveguides 40 and 41 are coupled on both the sides of the axis of the semicircular waveguide 34 without being coupled along the axis thereof. Therefore, the ring-shaped cavity resonators 35 and 36 and the rectangular waveguides 40 and 41 should preferably be coupled with the semi-circular waveguide 34 by the magnetic field generated by a transmitted electromagnetic wave which has two maximum amplitude portions at points 0.63R apart from the axis of the semi-circular waveguide 34 as measured on the basis of the radius R thereof, in place of the electrical field generated by the electromagnetic wave which has a single maximum amplitude portion extending along the axis of the semi-circular waveguide 34. For this purpose, the semi-circular waveguide 34, ringshaped cavity resonators 35 and 36 and rectangular waveguides 40 and 41 are so overlapped that the center of the coupling portion of the corresponding directional couplers is situated 0.63R apart from the axis of the semi-circular waveguide 34.

New let us explain the detail of the dimension of each constitutional part of the aforesaid wideband directional filter 30 where it is used as a channel dropper filter to be installed in each repeater for the millimetric wave band communication as shown in FIG. 2.

Both ring-shaped cavity resonators 35 and 36 are formed to have circumferences equal tointegral multiples of the guide wavelengths of the frequencies, for example, f 1 and f2 of the desired adjacent ones of a group of signals whose central frequencies fl, f2,f3 .fn falling within a frequency range of 40-80GI-Iz are successively different by 800MHz, so as to resonate with the frequencies fl and f2 of said desired adjacent signals.

The multi-holes 37 and 38 are bored in the ringshaped cavity resonators 35 and 36 at an interval substantially equal to a quarter of each of the guide wavelengths of the respective signal center frequencies f 1 f2. The ring-shaped cavity resonators 35 and 36 are each desired to be practically formed in the shape of an athletic field whose coupling portions with the semicircular waveguide 34 and the two rectangular waveguides 40 and 41 as are made straight, in order to enhance the degree of coupling therewith. On the other hand, the semi-circular waveguide 34 has a radius of about 5mm as will be clear from FIG. 6 and the rectangular waveguides 40 and 41 are formed to have a width w of about 3.9mm and a height h of about 2.4mm. The directional multi-slit arrangements 45, 46, 42 and 43 provided in the semicircular waveguide 34 and rectangular waveguides 40 and 41 each comprise, for example, three slits mainly functioning as a directional coupler which have a width l of about 1mm, the same length as the width of the respective rectangular waveguides 40 and 41, and an interval equal to substantially a quarter of the guide wavelength of a central frequency between the aforesaid respective signal frequencies fl and f2; and two slits mainly functioning as impedance matching elements which are disposed at both the sides of the directional coupling slits, and have about one half the width (in this case, about 0.5 mm) of that of the directional coupling slits. The rectangular waveguides 40 and 41 are respectively formed to have two ports.

Let us explain the case in which the wideband directional filter 30 according to the present invention so manufactured is used as a channel dropping filter in each repeater section of a millimetric waveband communication system shown in FIG. 2. As will be clear from FIG. 2 separate channel dropping filters are used reception and for transmission. For convenience, the operation of reception and transmission will not be described with reference to only one channel dropping filter.

When a group of signals f1 to fn composed as mentioned above are received from one port 341 of the semicircular waveguide 34, a signal component fl of the grouped signals, after being resonated by the associated cavity resonator 35, is derived from the predetermined port of the associated rectangular waveguide 40. Likewise, a signal component f2 of the grouped signals fl to fn is drawn out from the predetermined port of the corresponding rectangular waveguide 41 after it is resonated by the associated cavity resonator 36. The remaining composite signals f3 to fn travel through the other port 342 of the semi-circular waveguide 34 without any influence from the cavity resonators 35 and 36. Conversely, signals fl and f2 transmitted to the respec tive predetermined ports of the rectangular waveguides 40 and 41, after being resonated by the corresponding ring-shaped cavity resonators 35 and 36, are composed and transmitted through the semi-circular waveguide 34. Thus, a wideband directional filter device in accordance with the invention is constructed by the abovementioned six wideband directional filters 30 each provided with two cavity resonators having different resonance frequencies and cascade-connected, as shown in FIG. 4, in the respective receiving and transmitting repeater sections of FIG. 2, said cavity resonators sepa rating any two predetermined adjacent ones of a plurality of composite signals in reception and conversely composing said two adjacent signals in transmission.

According to the wideband directional filter device so constructed, multi-slits are used as directional couplers provided in the semi-circular waveguide and rectangular waveguides in place of the conventional multiholes as shown in FIG. 1. This arrangement offers the advantage of attaining a stronger coupling by fewer slits than the multi-holes. The results of experiments reveal that a 30dB bandwidth which bears the ratio of 2 to 3 percent to the central frequency can be obtained using a wideband directional filter device of this invention. It is therefore possible to obtain a wideband directional filter having a 3dB bandwidth of 800MHz at the central frequency of SOGI-Iz. When an E-plane coupling is formed by providing such multi-slitted directional coupler along the axis of the semi-circular waveguide as in the case of the multi-hold directional coupler of FIG. 1, then a plurality of spurious modes are undesirably generated from a practical viewpoint.

According to the present invention, the multi-slitted directional couplers are provided at both the sides of, and in a symmetrical relationship to, the axis of the semicircular waveguide as mentioned above. Therefore, all spurious modes generated at the two coupling portions of the semi-circular waveguide are opposite in polarity to each other and cancelled with respect to each other, thus effectively preventing generation of spurious modes. In addition, each wideband directional filter of the invention has the advantage of separating or composing two signals having different central frequencies. If, therefore it is necessary to cascade connect a plurality of channel dropping filter devices as shown in FIG. 4, the number of the channel dropping filter required can be halved with the result that the repeater section can be rendered smaller in size and power loss is prominently reduced. Additionally, the wideband directional filter device of the invention has the advantage that a semi-circular helix waveguide 50 having an excellent effect of suppressing generated spurious modes, as shown in FIG. 4, may be used as a transmission line between the respective channel dropping filter devices.

FIG. is a characteristic curve representation showing the degree of coupling between the semi-circular waveguide 34 and the two rectangular waveguides 40 and 41 and the experimental results of directionality obtained when the frequencies of received and transmitted signals are varied within the frequency range of 45--60GHz, under the condition where the semicircular waveguide 34 and both the rectangular wavegudes 40 and 41 are superposed, as shown in FIG. 6, except for the ring-shaped cavity resonators 35 and 36. In the characteristic curve representation the broken line represents a theoretical value and the solid lines show experimental values. To obtain a wideband directional filter having 3dB bandwidth of 800 MHZ at the frequency band of 40-8OGI-Iz, the degree of coupling between the semi-circular waveguide and both the rectangular waveguides is required to be about 5 to 6dB. As will be clear from FIG. 5 the wideband directional filter device according to the present invention having the experimental value substantially coinciding with the theoretical value can fully satisfy the requirement.

FIG. 7 is a diagramatic, perspective view, partly broken away, showing one modification of a completed wideband directional filter device in accordance with the invention. The ring-shaped cavity resonators 35 and 36 have only to be coupled with the corresponding rectangular waveguides 40 and 41 so that the directional couplers of the cavity resonators superpose on the corresponding directional couplers of the rectangular waveguides. From the viewpoint, this modification is arranged as follows. The rectangular waveguides 40 and 41 are respectively coupled with the outermost portions of the cavity resonators 35 and 36, but not with the mutually facing inner side portions thereof, as shown in FIG. 3, disposed below the semicircular waveguide 34. This modification is different in this respect from the embodiment of FIG. 3.

FIG. 8 shows another embodiment of a wideband directional filter device according to the present invention. With this embodiment branch-guide directional couplers 451, 461, 421 and 431 are provided in place of the multi-slit directional couplers 45, 46, 42, and 41 for the semi-circular waveguide 34 and rectangular waveguides 40 and 41 of the embodiment of FIG. 3. It

will be appreciated that the wideband directional filter device so constructed can be put to practice and attain the same results as obtain in the embodiment of FIG. 3. In the multi-slitted type, the thinner its plate thickness the better as far as its mechanical strength is maintained. In the branch-guide type, however, each thickness of plates 391 and 441 is required, as will be known, to be set at a quarter of the guide wavelength of the predetermined signal frequency. The experimental structure of FIG. 6 is applied to the wideband directional filter device of FIG. 8 with substantially the same effect as mentioned above, provided that the multi-slits of FIG. 6 are replaced by the branch-guides.

In FIGS. 6 to 8, like reference numerals are used to denote the like parts or elements of the embodiment of FIG. 3 and any further explanation is therefore omitted.

What we claim is:

1. A wideband directional filter device designed to separate in reception any desired signal component from a group of composite wideband signals having different central frequencies which are higher than that of the microwave region and conversely in transmission to compose individual signal components to transmit the composed wideband signals, the improvement wherein said wideband directional filter device, comprises: a semi-circular waveguide connected to a transmission line for transmitting said group of composite wideband signals; two ring-shaped travelling wave cavity resonators disposed in substantially the same plane and having the mutually facing inner side walls positioned below the flat wall of said semi-circular waveguide in substantially symmetrical relationship with respect to the axis thereof, said cavity resonators each having a circumferential length equal to an integral multiple of the guide wavelength of each central frequency of any two different signal components included in said group of composite wideband signals; two rectangular waveguides each having its wall portion disposed in proximity to the associated one of said two cavity resonators; and directional couplers disposed in at least the mutually facing wall portions between said two rectangular waveguides and said two cavity resonators as well as between said two cavity resonators and said semicircular waveguide.

2. A wideband directional filter device claimed in claim 1 wherein said cavity resonators each comprise two layers formed in the upper and lower walls of a single metal plate, and wherein multi-holes, functioning as a direction coupler between said semi-circular waveguide and said two cavity resonators as well as between said cavity resonators and said two rectangular waveguides, are bored in the partition wall of eachsaid cavity resonator at an interval equal to a quarter of the guide wavelength of the central frequency of the associated signal component included in said composite wideband signals.

3. A wideband directional filter device claimed in claim 1 wherein said cavity resonators each have straight extending wall portions which face said semicircular waveguide and said two rectangular waveguides.

4. A wideband directional filter device claimed in claim 1 wherein said directional couplers include multislits perforated in two portions on the flat wall of said semi-circular waveguide substantially symmetrical with respect to the axis thereof as well as in each predetermined wall portion of said two rectangular waveguides and disposed at an interval equal to substantially a quarter of the guide wavelength of the central frequency of the associated signal component included in said composite wideband signals. I

5. A wideband directional filter device claimed in claim 4 wherein said multi-slits comprise a plurality of said adjacent slits formed for mainly directional coupling, and two additional slits for mainly impedance matching perforated on the opposite sides of said adjacent slits and having about one half the width of that of said adjacent directional coupling slits.

6. A wideband directional filter device claimed in claim 1 wherein said directional couplers include multi-branch-guides positioned in two portions-on the flat wall of said semi-circular waveguide substantially symmetrical with respect to the axis thereof as well as in each predetermined wall portion of said two rectangular waveguides and disposed at an interval equal to substantially a quarter of the guide wavelength of the central frequency of the associated signal component included in said composite wideband signals.

7. A wideband directional filter device claimed in claim 6 wherein said multi-branch-guides comprise a plurality of said adjacent branch-guides formed for mainly directional coupling, and two additional branch-guides for mainly impedance matching positioned on the opposite sides of said adjacent branchguides and having about one half the width of that of said adjacent directional coupling branch-guides.

8. A wideband directional filter device claimed in claim 1 wherein said wideband directional filter device comprises a plurality of units cascade connected through a semi-circular helix waveguide and the two respective cavity resonators included in said directional filter device units are designed to resonate at the two predetermined central frequencies of the two respective preselected signal components included in said composite wideband signals. 

1. A wideband directional filter device designed to separate in reception any desired signal component from a group of composite wideband signals having different central frequencies which are higher than that of the microwave regioN and conversely in transmission to compose individual signal components to transmit the composed wideband signals, the improvement wherein said wideband directional filter device, comprises: a semi-circular waveguide connected to a transmission line for transmitting said group of composite wideband signals; two ring-shaped travelling wave cavity resonators disposed in substantially the same plane and having the mutually facing inner side walls positioned below the flat wall of said semi-circular waveguide in substantially symmetrical relationship with respect to the axis thereof, said cavity resonators each having a circumferential length equal to an integral multiple of the guide wavelength of each central frequency of any two different signal components included in said group of composite wideband signals; two rectangular waveguides each having its wall portion disposed in proximity to the associated one of said two cavity resonators; and directional couplers disposed in at least the mutually facing wall portions between said two rectangular waveguides and said two cavity resonators as well as between said two cavity resonators and said semi-circular waveguide.
 2. A wideband directional filter device claimed in claim 1 wherein said cavity resonators each comprise two layers formed in the upper and lower walls of a single metal plate, and wherein multi-holes, functioning as a direction coupler between said semi-circular waveguide and said two cavity resonators as well as between said cavity resonators and said two rectangular waveguides, are bored in the partition wall of each said cavity resonator at an interval equal to a quarter of the guide wavelength of the central frequency of the associated signal component included in said composite wideband signals.
 3. A wideband directional filter device claimed in claim 1 wherein said cavity resonators each have straight extending wall portions which face said semicircular waveguide and said two rectangular waveguides.
 4. A wideband directional filter device claimed in claim 1 wherein said directional couplers include multislits perforated in two portions on the flat wall of said semi-circular waveguide substantially symmetrical with respect to the axis thereof as well as in each predetermined wall portion of said two rectangular waveguides and disposed at an interval equal to substantially a quarter of the guide wavelength of the central frequency of the associated signal component included in said composite wideband signals.
 5. A wideband directional filter device claimed in claim 4 wherein said multi-slits comprise a plurality of said adjacent slits formed for mainly directional coupling, and two additional slits for mainly impedance matching perforated on the opposite sides of said adjacent slits and having about one half the width of that of said adjacent directional coupling slits.
 6. A wideband directional filter device claimed in claim 1 wherein said directional couplers include multi-branch-guides positioned in two portions on the flat wall of said semi-circular waveguide substantially symmetrical with respect to the axis thereof as well as in each predetermined wall portion of said two rectangular waveguides and disposed at an interval equal to substantially a quarter of the guide wavelength of the central frequency of the associated signal component included in said composite wideband signals.
 7. A wideband directional filter device claimed in claim 6 wherein said multi-branch-guides comprise a plurality of said adjacent branch-guides formed for mainly directional coupling, and two additional branch-guides for mainly impedance matching positioned on the opposite sides of said adjacent branch-guides and having about one half the width of that of said adjacent directional coupling branch-guides.
 8. A wideband directional filter device claimed in claim 1 wherein said wideband directional filter device comprises a plurality of units cascade connected through a semi-circular helix waveguide and the two respecTive cavity resonators included in said directional filter device units are designed to resonate at the two predetermined central frequencies of the two respective preselected signal components included in said composite wideband signals. 